Tubular structure embodying welded joint and method of making the same



March 7, 1939. 2,149,844

TUBULAR STRUCTURE EMBODYING WELDED JOINTAND METHOD OF MAKING THE SAME 2 Sheets-6B eat 1 Filed March 7, 1935 INVENTOR HARRY S GEORGE ATTORNEY Maz ch 7, 1939.

I H.'S. GEORGE TUBULAR STRUCTURE EMBODYING WELDED JOINT AND METHOD OF MAKING THE SAME FiledMarch 7, 1935 2 Sheets-Sheet 2 INVENTOR.

HARRY 5. GEORGE ATTORNEY.

Car ecu,

This invention relates to a welded joint and to a method for its production. More especially it concerns the production of an airplane fuselage, or similar welded truss structure composed of members or' assemblies which have been heattreated prior to the welding operation,--which welded structure has a strength adjacent the weld at least approximating the strength that would be possessed by it if it were heat-treated as a unit after the welding operation,

Although the present invention has a wide field of usefulness for general construction lliurposes, it is of special utility in the production of welded joints from heat-treated members of special alloy 5 steels, such'for exampleas the-chromium-molyb- 'denum steel and stainless steel seamless tubing widely used in aircraft manufacture for airplane fiiselages, where a high strength and light weight alike are essential, but where it is impracticable to heat-treat the welded assembly after its fabrication Heretofore, in the case 01 welded T-joints, lattice joints, and the like, normally loaded to high stresses near the joint, the required high strength generally has been secured by the selection tubing of ample size to provide an unheat-trea :1 joint of the desired strength, and/or by the use of gusset plates, straps, and the like. This results in a very substantial increase in the weight of the members composing the joint over that which would be required if the completed assembly could be heat-treated after. the welding operation; and there is an increase in the cost of material and labor. a

Welding reduces the strength of heat-treated tubing adjacent the welded joint because oithe resultant local tempering efiect of the welding heat. A line or zone of weamess is formed extending parallel to the line of the weld and spaced therefrom. In a series of tests upon various welded T-joints and lattice joints made of tubing oi chromium-molybdenum alloy, this line of weaknesslay about ,5 inch from the weld and coincided with a zone of minimum hardness "of the base metal.

In accordance with the present invention, additional strength is imparted to the welded strucmm at and adjacent the joint while limiting the weight or the various members composing it.

This is accomplished by enlarging the diameter of the ends of said members and/or by increas ing the total cross-sectional area of metal at such ends which are to be joined to other members by welding.

Among the more important objects of the in= as N. $2., designer, to Won (Carbide and a to all {New i 2 Ne. 9,695

tion; to provide additional strength to a struc 5 ture-adjacent a welded joint while limitingthe weight of the structure; to provide a novel welded structure formed of alloy steel members hardened by heat treatment or cold wormng before welding, the strengthof which structure is substan- 10 tlally undiminished by the welding operation; to provide a novel welded structure composed of cold drawn members of heat-treated alloy; and to provide cold drawn tubing adapted for use in the manufacture of the said welded structure, 16 successive portionsof the length of which tubing have different well thicmesses and/or difierent diameters.

In thepractice of the invention, the end of each of the tubes forming the joint is provided 20 thereat with an expanded on enlarged portion or member, and/or one having suiiicient cross-sectional area of metal that, when the said ends are welded in place to form the joint, the zone or line of weakness, 1. e.,--the so-cailed "annealed 5 ring,-will fall within such enlarged portion or, member, and this unheat-treated portion will have a total strength as great or greater than those heat-treated portions not afiected by the welding operation, or which will approach such 30 strength as nearly as may be desired.-

Referring now to the accompanying drawings which illustrate my invention,

Fig. 1 is a side elevation of a T-joint assembly embodying the invention; 5

Fig. 2 is a section taken along the line 2--2 of Fig. 1, looking in the direction of the arrows;

Fig; 3 is a side elevation of various unassembled element's shown in the assembly of Fig. 1;

Figs. 4 and 5 respectively, are side elevations of 4c modified Joint assemblies formed from tubing having enlarged ends;

Figs. 6 and 7 are fragmentary longitudinal views whichillustrate forms of cold drawn tubing having reinforced ends of increased wall 45 thicess;

Fig. 8 illustrates somewhat diagrikj uatically a step in the cold drawing of tubing;

Fig. 9 is a side elevation of tubing having 5G spaced enlarged portions, parts being broken y; a I

Fig. 10 is aside elevation of a lattice joint assembly embodying the invention; and llis a ptive view of an n fuselage embodying the invention, parts being broken away.

The improved joint of the present invention preferably comprises heat-treated tubular structural members of hardened metaLeach havin an end portion or extension of increased total cross-section of metal adjacent the joint. The area of the said end portion or extension is such that when the members are welded to form the joint, the annealed ring", constituting the zone of greatest weakness in the structure, will lie within the area of the enlarged end portion. Therefore, by virtue of the resultant distribution of stresses applied to the joint over the larger cross-sectional area of metal of the end portion, the'portions of the welded joint which heretofore have been known to have the minimum strength and hardness of base metal may be made as strong or stronger than the remainder of the tubing. The portions of the heat-treated hardened metal tubing remote from the welding zone need be only of suimcient size to resist the stresses normally encountered at such points.

In the modification shown inFigs. 1 to 3, the joint comprises a sleeve H, of suitable metal or alloy, open' at both ends and adapted to house more-or less snugly therein the enlarged end portions of tubular members l3, Id of steel or alloy, which may form the struts or longerops of an airplane fuselage or other structure. As shown, these enlarged end portions are in the nature of tubular collars or bushings I5, it. The outer diameter of each bushing I 5 is such that an end of the latter extends into and fits snugly within the passageway in the sleeve ll.

The opposite ends of each bushing I5 is shrunk on and/or welded to an end of a tubular member l3, l3, preferably by a modification of the oxy-a'cetylene process or an equivalent weldin process. The end margins of the tubular members l3 may, if desired, be expanded for the purpose. The end margin of each bushing ill at the line of the weld i1 joining the members l3 and I5 may be staggered, as shown, for increasing the length of the annealed "ring, so

as to distribute the latter over a considerable area and deconcentrate the lines of weakness. The end margins ofthe sleeve H may be staggered for a similar reason, to provide staggered lines of weld 28, preferably parallel to the lines ii.

The joint also may comprise one or more metal or alloy bracing struts or tubular joint members l9, each having a bushing 2i welded thereto at one end along a staggeredline of weld 2d. The end of the bushing 2| is shaped to fit closely the curved outer surface of the sleeve H, as shown in Figs. 1 and 2.

In' the fabrication. of this form of joint, the respective bushings IE, i5, 2! first are welded to the corresponding tubular members, it, l3, is. These welded structures then are heat-treated to increase their strength and hardness. The joint is then formed by assembling the members l3, is, in the sleeve H, welding the bushings to the sleeve along the ig-sag lines 28, and then welding the ireeend c f'bushing 2% to the midportlon of the sleeve at the desired angle, along the line of weld 25.

If desired, a single, continuous tubularmemher it may be employed, having a slip-over sleeve ll welded thereon at a selectedjoint midway of its length, and the welded area heattreated. A bracing strut or member is, having welded thereon an enlarged bushing 25, may then be welded to the sleeve H in the manner described above, to provide a joint ct great strength adjacent the line 0! weld even in the absence of special heat treatment.

The following will exemplify the invention:

A reinforced T-joint of the type shown in Fig. 1 may be made from chromium-molybdenum seamless steel tubing l3, having an outside diameter of 1% inches, and a wall thickness of .049 inch, and which when heat-treated has a tensile strength of 130,000 to 150,000 pounds per square inch. The bushing members l5 employed have outside diameters sufficiently large to slip freely over the 1% inch x .049 inch tubing.- They also have wall thickneses providing metal,possessing a" strength of at least around 90,000 pounds per square inch as welded,in amount sufflcient to produce a final tube and joint having a strength at and adjacent the weld equal to that of the heat-treated tubing is of smaller diameter.

The bushings l5 first are welded to the tubin it in the manner described, and the composite structure then isheat-treated to increase the tensile strength of the tubing. The heat treat.-

as the diameter and wall thickness of the strut member is; l I

In a modification of the invention employing cold drawn metal or alloy tubing for the elements of the joint, the use of a sleeve II for purposes of assembly of the joint is unnecessary. Illustrated in Fig. 4 is a continuous longeron Id of cold drawn tubing having an intermediate section 25 of increaseddiameter, and preferably also of increased wall thickness, though the latter is not essential. Secured to the longeron at the section 25 thereof are strut members it, havmg enlarged end marginal portions 20 welded to the section 2'5 of the former. Acetylene welding is preferred for the purpose.

Another form of construction is shown in Fig. 5, wherein numeral 21 designates an enlarged end portion of cold drawn tubing i3 having its end margin 28 staggered or zig-zag as shown. An enlarged end portion. 29 of a second cold drawn tubular member It is adapted to be insorted within the portion 21 of the tubular member l3 and to be secured therein by welding along the margin 28 of the latter. The strut members 88, it, are then welded to the enlarged portions of the members It, 83' in the general manner hereinbefore described. The enlarged end portion 21 has a greater total cross-sectional area oimetal than the enlarged end portion 29.

Figs. 6 and 7 respectively illustrate two forms or cold drawn tubing having enlarged or reinforced end rtions, and suitable for use in the present invention.

'The tubing shown in Fig. 6 may be shaped by cold-drawing it in the following manner:

The tubing I3 is cold drawn to a final end size desired for the large end margins 25. A split die 30 (see Fig. 8) is then placed around the tubing also,

1 member 33, thusswaging the tubing at thdie and drawing the tubing through the die.

5 it swae'ing and drawing operation is then repeate until the swaged portion of the tubing is of the desired outside diameter and length. The is then ready for use; or it can be cut into suitable lengths. V

The swagingand die-drawing of the tubing may be discontinued at selected spaced zones, during the movement of the tubing past the die induced by the draw chuck. Thus are produced enlarged zones 86, separated from each other by tubular zones it of smaller diameter formed by action of the die 39, as indicated in Fig. 9.

Fig. 7 illustrates a fonnoii metal tubing having reinforced ends of increased wall thickness, but wherein the outside diameter at the ends is substantially thesame as that of the midportion oi the tubing. This tubing preferably first is heat-- treated, after which the reinforcing and connecting member is welded tothe thick end portions of the tubing.

Fig, 10 illustrates one application of the invention to the construction of a lattice joint suitable for an airplane fuselage. The longerons it have welded bushings 55 secured within the sleeve ii, and the welded zones heat-treated. The construction of this joint is very similar to the coin struction shown in Figs. 1 to 3.

Each of two lateral tubular struts to has a corresponding bushing d2 of greater diameter, secured thereto by welding followed by a heattreatment of at least the zone adected by welding. The free end of each bushing 532 is shaped to closely engage both a portion or the curved surface of the sleeve ii and a portion of the adjacent containing surface of the other this 32. me contacting surfaces of the hushmgs and sleeve are intimately joined by acetylene welding or its equivalent, as illustrated. a

Fig. 11 illustrates one form of airplane fuselage produced in accordance. with the invention, util izing welded joints of great strength, the resultant truss structure having substantially the some weight and strength as are possessed by a as structure hardened as a unit by the same heat treatment following the various welding opera- Mons-thereon. Heretofore, attempts to harden such a trims structure. as a unit have been unsatisfactory, since the heat-treatment of the en tire unithas invariably resulted-in warping of the truss members during the treatment- Prior to theirv assembly to form the fuseiese, the various longerons 5E2, cross members t2 and 5t, diagonal strut members 5d, and vertical mem hers so, illustrated in Fig. 11, preferably are shaped as desired and their enlarged ends are prepared and hardened in suitable manner as hereinbefore disclosed. In the modifications shown in Figs. 1 to 3, and lo, the horde treatment isgiven after the bushing members it, t2, have been welded to the said longerons, struts, and other truss members, and before their assembly The invention is adapted for use with other fuselage designs than that illustrated, and other arrangements of members forming the welded joints may be employed in aceordance'with the invention without departing from the spirit thereof. Thus a welded tubular structure of anv size is made possible, comprising a plurality of welded joints and a. plurality of members previ ously hardened by heat treatment or cold wor before welding, which structure has r. tsntislly lateral ular structured member r'; .134'11 and weight as a,

' time which had been-hardened as a unit, by the oi the present invention may not require the use throughout of the particulartype of welded joint herein descri. At points where a high strength-weight r'atiois not vital, some form of joint of the types used prior to my invention may be employed.

. It is'within the purview of the invention to use either the same or difierent ferrous or nonierrous metal alloys in iabriwting the various elements of the joint structure, for controlling the Physical and chemical properties of the members forming the joint. us, a metal or alloy may be selected for the sleeve M which, while having satisfactory strength and toughness, is especially resistt to the tempering action of the heat applied thereto during the welding operationor which possesses properties which at least par tiaily onset such tempering sheet.

The present invention successfully compen-- sates for the loss of strength occurring at joints formed of a plurality of members, due to the efi'ect of heat produced therein during a welding or similar operation, particularly when using heat-treated members made of chromium-molybdenum and similar alloy steels.

The invention is susceptible of mcation within the scope oi the appended cl.

1 claim:

l. A welded joint comp a tubular member of hardened metal, the said member having an expanded portion of greater total cross-sectional area of metal than the remaining portion thereof, and at least one lateral tubular member having an enlarged end welded to the'flrstnamed memher a tthe said expanded portion.

2. A welded joint comprising two aligned tubular metal structural members, each having welded thereon a bushing member of greater diameter than either oi the said tubular members and of at least as great a cross-sectional wall area as the latter, each of the resultant welded assemlilies having been hardened after the said welding operation, and a tubular metal sleeve welded at its respective ends to a corresponding one of the said bushings, the said sleeve and bushings being as strong adjacent the welded area without subsequent heat treatment as are the portions of the tubular members remote from the welded areas and which were unaflected by the Well taperation.

3. A welded joint comp. two aligned spaced tubular metal structural members, each having welded thereon a greater diameter and greater wall ckness than oil or the said tubular members. at least the zones aflected by the said welds hardened, and a sleeve welded at its respective ends to'a corrwpon one of the said bushings along a seared line in iii-welding zone, and at least one welded to the sleeve midway of its ends.

4. A fuselage for aircraft, comp a pin rslity of welded" joints, at least one of the said joints being formed-of a tubular member of hardened metal having a portion of greater crosssectional ones of thereof, and at least one lateral tubular member he on eed end welded to the t-named member atthe said i e O ster cross-T seetional V I metal adjacent portions 5. A fuselage for aircraft, comprising a pinrality of welded joints, at least one of the said joints being formed of a tubular member of hardened chromium-molybdenum alloy steel having.

are substantially undiminished by the welding operation, and comprising a plurality of welded joints, at least one of the said joints being formed of two aligned spaced tubular members of hardened chromium-molybdenum steel, each of the latter having an end portion of enlarged diameter, and a reinforcing and connecting sleeve member of chromium-molybdenum steel having a diameter at least as great as that of the said end portions of the first-named tubular members, the said connecting member being welded to each of these end portions, and at least one lateral tubular member of hardened chromium-molybdenum steel having an enlarged end welded to the said sleeve member.

7. .The process of producing a welded Joint adapted for use in airplane fuselage construction, which comprises welding an end of a tubular metal bushing to and around an end of a tubular structural member, hardening the said member and bushing assembly at least adjacent the welding zone, inserting the free end of the bushing in a tubular sleeve, and welding the bushing and sleeve together.

8.-The process of producing a welded joint adapted for use in airplane fuselage construction, which comprises welding an end of a tubular metal bushing to and around a tubular structural member of smaller diameter aligned therewith, hardening the assembly of the said member and bushing at least adiacent the welding zone, in-

serting the free end of the bushing in a tubular sleeve, welding the bushing and sleeve together,

and thereafter welding at least one lateral tubular structural member to the said sleeve.

9. The process ofproducing a welded joint adapted for use in airplane fuselage construction, which comprises inserting an end of a tubular structural member within .an expanded end portion of a second structural member aligned therewith and having an irregular end margin, welding the two members together alongthe line of the said end margin, hardening the resultant assembly, and thereafter welding to the expanded portions of both the first-named and the secondnamed members at least one lateral structural member having a reinforced 'end portion, with the latter directly-welded to the said expanded portions.

10. The process of producing a welded joint adapted for'use in airplane fuselage construction, which comprises inserting an expanded end of a tubular structural member within an expanded end portion of asecond structural member, the last-named end portion having a greater total crow-sectional area of metal than the firstnamed member and being aligned therewith, the said second member having a staggered end mar-.- gin, welding the two members together along the line of the staggered end margin, hardening the 7 resultant assembly at least adjacent the line of the said weld, and thereafter welding to the ex- 'panded portions of both the first-namedand the second-named members at least one lateral structural member. having areinforced end'portion, with the latter directly welded to the said expanded portions.

v 11. The method of preventing loss of strength in welded joints due to the heat-tempering effect of a welding process, which comprises providing the adjacent ends of each of two aligned space heat-treated metal tubular members with expanded heat-treated end portions of greater diameter than the midportion of the said members and of suficient wall thickness that'when the said expanded end portions are welded to a tubular structural member having a total cross-sectional area of metal at least as great as that of the said end portions, the resultant joint will be at least as strong adjacent the unheat-treated welds as is the portion of the heat-treated tubular member remote from the welds, and thereafter welding an expanded end portion of each of the said aligned tubular members to the said tubular structural member. 1

12. The process of producing a strong welded joint, which comprises welding to an end of each of two tubular members forming the said joint a corresponding collar of larger diameter than the diameter of the said tubular member to which it is welded, hardening each of the resultant welded assemblies, and thereafter welding the free end margins of the respective collars within a tubular reinforcing and connecting sleeve.

13. The process of producing a strong welded ioint, which comprises welding to an end of each of a plurality of tubular members forming the said joint 9. corresponding collar of larger diameter than the diameter of the said tubular memher to which it is welded, heat-treating the resultant welded assemblies, inserting the free end margins of two of the respective collars within a tubular reinforcing and connecting sleeve, weld-' drawing the swaged tubing through a die in a direction away from the said end thereby reducing the diameter at the die-drawn portions of the tubing, thereby producing a cold drawn tubing having an end zone of selected greater diameter than the selected diameter of the intermediate portion, and welding to the tubing at the said zone at least one structural tubular member having an enlarged end-portion, with the lastnamedportion directly welded to the" tubing at t the said end zone.

7 \15. In the process of producing a welded joint of cold drawn tubing, the steps which comprise cold drawing metal tubing to a selected flnal end diameter and metal thickness, swaging the tubing at a selected point near an end thereof, drawing the swaged tubing through a die in a direction away from the said end, thereby reducing the diameter and wall thickness of the die-drawn portions of the tubing and producing a cold drawn tubing having an end zone of selected diameter and wall thickness greater than the diameter and wall thickness of the die-drawn portion, swaging' the tubing at a. second point spaced from the said die-drawn-portion, drawing the 1 the enter and t tile-drawn portion the tubing, concreting the tubing into selected lengths at the resmctive portions of the tubing inediete odjeeent die-drown portions thereof, d @1111; to the tubing at the said zone at least one etmctnroi tubular m he on end-portion, with the portion directly Welded to the tubing at the sold end none.

16. A wet joint for airplane iuseinee construction, which comprises two aligned heat-treated tubular embers oi hardened elloy steel, the end rtions of each r .w oi mentor dieter then the interm portion thereof, and e reinforcing and connecting sleeve having o oieter greater than that of the said end portions of the tubuler ms, the said connecting sleeve ends to the said end L rtione, the said end portione of cient thicmess to give d at after welding but without subuent heot-treetnt e totcl etre nt equal to that oi the said intermediate portion of the tubulnr mber. 1

17. it welded Joint structure to of 0. steel members each 1 ened as a unit before welding to form the sold structure, the strength of which '11 is substantielly hy the said welding operation, which structure comprises two aligned spaced tubuielr rs i of hardened motel having weicied thereon enlarged end portions, the said mom end end portions having hardened es 3, unit after the welding operation, a, reinforcing end connecting sleeve oi hardened mete! heving end mrtions surrounding the respective enlarged end portions of said tubular members welded thereto, the said sleeve and said end portions of the tubular members having walls of sumcient thi'cmess to give them, after the tweiding operation, a strength at least as t members into 'In' @1 ate to aid .es that of the portions of the hardened tubular 

